1. Field of the Invention
The present invention relates to a method of controlling an easing roller included in a loom to execute selectively a position control operation or a tension control operation by an easing motion.
2. Description of the Related Art
An easing roller control method disclosed in JP-A No. 4-24244 controls the position of an easing roller by supporting each end of the easing roller for rotation on each free end of a pair of arms fixed to the output shaft of a drive motor, and controlling the turning angle of the output shaft of the drive motor. When a let-off tension control period is ended and an easing control period is started, the mode of control operation for controlling the drive motor is changed from a tension control mode to a position control mode. The easing roller is shifted by a desired distance set by operating a setting device toward the cloth fell at the beginning of the easing control period. The position of the easing roller thus determined at the beginning of the easing control period is dependent on the position of the easing roller determined for tension control in the tension control period preceding the easing control period. Thus, the position of the easing roller at the beginning of the easing control period varies for each weaving cycle of the loom; that is, the most advanced position of the easing roller, which, generally, is the position of the easing roller at a beating-up moment when the phase of the main shaft of the loom is 0.degree., varies for each weaving cycle of the loom. Thus, it is possible that the easing roller is required to move to an unexpected position depending on the condition of tension control and cannot be shifted to that required position, and satisfactory tension control cannot be achieved.
An easing motion disclosed in JP-A No. 7-238443 uses a cam mechanism to drive an easing roller for easing warp yarns for forming satin stripes. This prior art easing motion is free from disadvantages of the above-mentioned easing motions. Since the warp tension is dependent on the cam contour of a cam included in the cam mechanism, it is virtually impossible to adjust the actual warp tension to a desired warp tension because the operation of a control system is disturbed by disturbance and the warp tension varies.